1. Field of the Invention
The present invention relates to fiber-reinforced molding compositions having superior mechanical properties which are based on polyphenylene ether resins, and also to a process for the preparation of these molding compositions.
2. Description of The Background
Polyphenylene ethers (PPE), also known as polyphenylene oxides, are polymers having a high heat resistance and also good mechanical and electrical properties. As a rule, they are used as blends with polystyrene resins, for example, DE-C-2,119,301 and 2,211,005 and/or polyoctenylene (DE-A-3,442,273 and 3,518,277).
Many attempts have been made to increase the rigidity of PPE-containing molding compositions by admixing reinforcing fibers composed of inorganic or organic material in the resin. For instance, DE-A-2,364,901 discloses polymer mixtures of PPE, polystyrene resins and glass fibers, the glass fibers used in this case having a length of between 3.1 and 25.4 mm, preferably of below 6.35 mm. EP-A-0,243,991 and the corresponding U.S. Pat. No. 4,749,737 describe the mixing of very short, unsized fibers with Si-H bond-containing siloxanes, to improve the fiber-matrix adhesion in the composition, followed by mixing in the melt with PPE and a polystyrene resin.
A specific modification of the fiber surface by treating the glass fibers with vinylsilanes or gamma-glycidoxypropyl-trimethoxysilanes for use in PPE-containing molding compositions is described in DE-A-2,132,595, JP 73/97,954, JP 74/10,826 and JP 85/88,072. DE-A-2,719,305 proposes the opposite method, i.e. end-group modification of the PPE via a silylation carried out before compounding. This technique however is a roundabout and labor-intensive method of achieving an improved fiber-matrix coupling.
A commonly used surface modification of the reinforcing fibers is achieved by treatment with aminoalkylsilanes, for example gamma-aminopropyltriethoxysilane. Glass fibers which have been sized in this manner are incorporated in numerous PPE-containing compositions, it always being necessary to additionally modify the composition of the thermoplastic matrix to bond the fibers to the matrix. For instance, JP 87/15,247 describes the addition of, for example, maleic anhydride-modified polypropylene. JP 85/46,951 describes the addition of ethylene-maleic anhydride copolymers and JP 85/44,535, DE-A-3,246,433 and JP 82/168,938 describe the addition of styrene-maleic anhydride copolymers. However, these polymeric additives have the disadvantage that they reduce the heat resistance of the molding compositions or else they are only partly compatible with the PPE matrix or in most cases are incompatible and therefore impair the mechanical properties of the molding compositions. A need continues to exist for a PPE based molding composition of improved mechanical properties.